Is she close to lambing? If so, I'd probably try to give her everything she needs close by so she doesn't need to do much walking. And I certainly wouldn't be tipping her up to trim feet, but if you can do it with her relaxed and comfortable standing, and support her as you lift her foot, then if you're sure you know what she needs and that she needs it now, before she lambs, then ok.
Any woman who's been pregnant will tell you that as you get larger, your feet *hurt*! And carrying triplets, your ewe will really be feeling the extra weight. It's very common to have (mentally or physically) marked a ewe for a pedicure once she's lambed, because she seemed a bit - or a lot - lame beforehand, only to find she's 100% sound the minute the lambs are out.
The way you're describing her leg looking bendy, I think I might, once she's lambed and sound, still try to work out what could have happened, and depending on what you find, be open to not breeding from her again. Having had triplets once she's quite likely to do it again, and if there's something about that leg that can't take the weight of near to full term triplets, then she's maybe best not asked to do it again.