But why did she have that can on her?
Because it's funnier/faster to just have her with the can in hand that do some more pannel where we see her leave her gf alone to walk out, get the can, walk back in, cuddle back with her gf while spraying the bug ?
From a narrative point of view, it flows better to just have her pop the can out of thin air. If only so she can play out the whole "cling endelessely" card. Same thing with how she says she went to flush it down the toilet while we didn't see it and it looks like they didn't move an inch in-between.