I see petco has petro-malt, I'll pick some up tomorrow.

even though she has been constipated in the past, I would be very careful
trying to treat this at home.  cause A) she might not be constipated, she
might have a urinary problem.  Unless you are 110% sure she is peeing as she
has been, this is of great concern.  b) if she is constipated and it stays
that way for a long period of time, she could do some damage to her colon
straining to get it out.  Once the damage is done, it is next to impossible
to undo (risky surgery) and she will continue to have this issue.

If this were me, I'd get her to a vet.

olive oil will be digested, to treat constipation you need an oil that is
inert like paraffine-oil, but there are enough anti-hairball-products
commercially available that you can use