Gabi was spayed last April but is still getting unwanted male attentions at the time that she would have had a season. Is this normal? is there anything I can do to stop it?

This happened to a friend's bitch, and it was because there was some ovarian tissue left behind at the time of the spaying. If the ovaries were active at the time (was she spayed near her season?) the surgery is more difficult and tissue can be missed. Gabi may need repeat surgery to find and remove the tissue.

Gabi's season was in Feb and op in April. Should have been ok.

If tissue was left behind does this mean that she could still become pregnant?

Yes, with that timing it's probably not the reason for tissue being left behind, but remaining tissue is still the most likely cause.

Edit: she won't become pregnant because she has no uterus, but could still have a phantom.

Some bitches do remain "hot totty" after spaying, my bitch is extremely attractive to the chaps (much like myself) :D  she does not have phantoms or anything else but was "hot stuff" prior to spaying too........ :D

Ditto...except I am considerably 'hotter' than my Cassie!!!! LOL :D :D :D  And I've had 'ALL' me bits out! LOL