How many times can a woman do an abortion before its dangerous? With consideration that she never gave birth before..

As few as required. It's a difficult question; there's no "safe" or "unsafe" line you cross. Most 1st trimester abortion is very safe, some women have 3-4 and are fine. But, some have problems after 1 . If an abortion is necessary you must decide, but if it's more than once or twice you might think seriously about prevention.