I wonder how to erase her legs so that she can wear her new leggings properly. The devices that I use to get rid of the legs just leave a white blob, so that doesn't work.

Go to Wardrobe>Click "Base" on the header bar>Toggle off "Left/Right Leg/Foot/Toes" under the "Limbs section"

[edit] Here, I made a picture guide

- If the background used has your avatar included then removing the legs will leave that space empty. You can try using another background to fill in where the legs are missing but it would need to be a full one without an outline for your avatar. hope this makes sense

Some backgrounds can be a pain to try to work with in that aspect.

I used both your suggestions and I am happy with the results. Thank you both very much.