DD first mentioned shaving her legs at 11, she popped a cossie on and I showed her how to do it safely. We talked about different methods, talked about doing it for you not for anyone else, I prefer to shave as I prefer the feel turns out she's quite happy leaving it and that's quite the norm nowadays. We talked about how if you leave underarm hair it can trap sweat and be more smelly so to make sure to wash really well with soap. Talked about what to do if you nicked yourself and a quick minor first aid reminder and that was it.
Just because many of us were left to our own devices and probably just pinched Dads razors doesn't mean that's the way it should be. Like any other stage of growing up give them options, the skills and then leave it up to them to make their own informed decisions.
Personally I wouldn't leave her to ask, even if you have a great relationship many teens find anything to do with growing up awkward and wouldn't feel able to ask. I personally never felt able to ask anything even though my mum was very approachable but she'd had a hysterectomy young and didn't remove body hair so I found it difficult talking about those things and I think because her mum died before she reached adolescence she didn't really know how to have those conversations as she had just been left to it, ironically I ended up as a science teacher teaching puberty and sex ed as part of my day job. I've always talked very openly with DD about periods, puberty etc and she often asks me questions she says others couldn't ask their parents and ones which I certainly wouldn't have asked mine which is great.
So, I would preempt it, maybe next time you are in the Supermarket together and down the toiletries aisle spark a convo of would you like to try.... Or put her together a basket of various toiletries as a gift, my DD loves anything to do with skincare and looking after her skin so you could put her a little something together with various items, facemasks, maybe some new period pants, selection of sanitary towels, tampons etc so she can try other things and it's just not focused on hair removal.