Hi there SeanHunkius, and welcome to the boards. I'm sorry to hear that you're in a situation where you're feeling down about your body, but glad to hear that you feel that you can speak with us about this, it is Scarleteen is a safe space for people to ask these kinds of questions.
It sounds like for both you and your cousin, her reaction to what I can assume was an overly harsh soap when cleaning her genitals was a unsettling experience. Unfortunately a lot of people don't know that they need to use only gentle soaps or just warm water, or because of societal stigma about these areas being more "unclean" that come from various hangups about sex that are false but exist in a lot of cultures, rather, the skin in the area is just more sensitive, like that around your eyes.
Given you have mentioned that you're not sexually active, and what you've described, you are likely not unwell, but rather have some irritation or pimples that can be cleared up on the skin in your genital area. Whilst people most generally associate pimples with the face, your skin has pores that can get dirt/sweat/old skin cells in them anywhere, which is what causes pimples. The other common cause of this kind of irritation on the genital area is if your family uses a scented detergent or dryer sheets on loads of washing that contain your underwear or other clothing that sits near your crotch area, the more sensitive skin on your body, like the genitals, are more likely to get irritated by these.
The good news is that you don't need to do anything harsh to clean your genital area and gentle washing should help deal with and prevent any pimples. Here are the instructions from one of our
advice articles (which advised a user who was over-washing their genitals. From your description of yourself, I have inferred that your body has a vulva, apologies if this is mistaken or you prefer to use other vocabulary than the medical terms for your body parts. If your unfamiliar with all of these words, we have a good explainer here that is suitable for people of any gender who have a vulva:
Innies & Outies: The Vagina, Clitoris, Uterus and More
The way to take care of your vagina and vulva when it comes to hygiene is just to wash the external vulva -- your inner and outer labia, your mons, around your clitoral hood, perineum and anus: all the bits you can see on the outside -- very gently, either just with warm water or water and a very gentle, unfragranced soap (certainly not any kind of deoderant or antibacterial soap) no more often than you wash the rest of your body. To wash, you can either just use your fingers or a soft washcloth: you don't want to be rough with the delicate tissue there. You don't want to try and wash inside the vaginal opening at all: leave that be, as it both takes care of itself and needs to be left alone to do that.
Other things you can do whilst things are clearing up (which pimples will over time with the introduction of gentle washing, even with just water and a cloth), is to wear breathable (not synthetic) underwear (like cotton, bamboo) and try wearing looser clothing that isn't to tight around the underwear area, like a looser short or pants, as opposed to tight jeans or exercise leggings. This reduces the sweatiness and friction in the area. Of course if things only get worse or don't change after a few weeks, that then could be the time to speak to a doctor or sexual health clinic about getting a topical cream to assist with clearing things up/help with the irritation if it's a reaction to a detergent used on your underwear or similar. This is something that many many people deal with in their lifetimes, so definitely doesn't make you different or "gross" compared to other people. You are person with a body, and sometimes our bodies react to things we'd prefer they didn't, which is very annoying, but also very normal.
If you also know that scented detergents or drier sheets are being used in your house, this would be something to talk to your Mom about changing if they are the cause. You mention you expect your Mom would be mad about you not coming to her earlier, when you say this, would you feel comfortable explaining to us what you expect to happen in terms of her expressing this?
This would involve thinking about your prior experiences where your Mum expressed a similar sentiment: would you expect if you told her it be more of an awkward/embarrassing situation of having to listen to her express this sentiment (and perhaps she would use a 'lecturing' tone), or would it lead to her mentioning it a lot/treating you differently/being huffy for a while, or would her anger be yelling and aggressive behaviour that would be emotionally and/or physically unsafe for you? I ask because depending on how the situation would happen, we would then be able to help with strategies to approach broaching the subject in a way that you can feel a bit more comfortable, or help you stay safe, does that make sense?
I hope this all helps you feel a bit better and gives you some useful practical information!