If she's immediately moving to a correct latch, after the slurping, you might just tolerate it for awhile. My DD2 was the same way, and she stopped doing it all on her own around six or seven weeks old. It was way too much trouble to keep unlatching her since within a second or two, she'd corrected the latch. (If I'm reading your siggy correctly, your baby is about a month old, right?) But if it's really bothering you, you can try to coach her to open her mouth wide before latching by tickling her lips or cheek, or showing her by opening your own mouth wide and making a funny sound like "ahhhhhhhhh" when you do it.