Do diapers....that will protect your carpeting etc.
http://www.sassypup.net/Belly-Bands-...p-1-c-357.html
You can attach women's thin sanitary napkins to these diapers and dispose as needed.
As for spaying her....I believe 4lbs should be fine to spay but hopefully someone here can confirm that. Zoe wsa 4.5lbs when she was spayed.