My sister has 2 kids and wants to avoid pregnancy without having any surgery - what is the best form of prevention that has the least side effects?

IUD. If the goal is to avoid surgery but have great birth control, the IUD is a good option.The insertion is uncomfortable & cost is pricey, but you get 3 or more years of use with <1%b failure rate/yr.
Other choices. Forms of birth control without significant side effects are: diaphrams, condoms, and spermacides.

Related Questions

My sister has 2 kids and wants to avoid pregnancy without having any surgery - what is the best form of prevention that has the least side effects?

All kinds. There are many types that work well for the busy mom. Nexplanon (subdermal implant) is good for 3 years. Mirena (levonorgestrel) & paraguard iuds are good for 5 & 10 years. Essure is permanent and all of the above are easily & quickly done in the office setting. (ps - so's a vasectomy...). Talk to your doc & see which is best for you. Read more...
Abstinence. All forms of birth control have some side effects or possibilities of getting pregnant. This includes iud, condoms and so forth. The method with the least side effects which is most effective would be abstinence. It is also the least likely to be adhered to. Read more...