Cows can certainly get mastitis pre-calving but I'm not used to thinking of it in sheep.
However, being footsore when heavily pregnant affects every species...
And yes, tipping over close to lambing not advised if not essential.
99.9% of apparently sore feet peri-lambing are better, with no attention, once lambed. Maybe subclinical with the extra weight off, but often you can't see any problem if you look, so I'd probably keep a watching brief unless she's struggling so much she is in danger of not eating enough (in which case, give her cake and hay so she doesn't have to move about all the time grazing - but do make her do some exercise because being stationary isn't good for them either.) If you do decide you need to take a look, it can be better to lift one foot at a time, like a horse, if you've got a helper can steady her for you.