Gift idea for Mom - thoughtful, or completely rude?

I am very close with my Mother in Law. She has taken up walking as a serious hobby (she goes walking a few times a week with friends), so I thought a really nifty pedometer could be a cool, practical gift.

However, the reason she goes walking is because it is a fun new way for her to get exercise and lose weight (which, in my opinion, she doesn’t need to – she looks great). Would it be rude to give her a gift that is related to her weight loss process?

Would a gift like that say “Hey mother-in-law, here’s a cool thing that could make your new hobby more fun!” Or is it likely that she would misread it as “Hey fatty, here’s something that will help you in your de-fattening process.”

I feel like exercise-related gifts are tricky. Yes or no to this idea?