The male will be aggressive towards female when he is ready to spawn and she wasn't.
Hello; I have a similar situation with a pair of angel cichlids. Several months ago I picked up two juvenile angel fish with one being a bit larger than the other. Had no idea they were male and female.
Things went well for many weeks and they got along. Around the time they were getting large enough to move out of their grow out tank they spawned on a plant leaf. I emptied the larger tank of other fish and placed the pair in. I expected them to continue to get along but that did not happen.
The male began to harass the smaller female to the point she was hiding pretty much all the time. I did in fact separate them for many weeks in order to feed up the female. Had to do this twice before the female had sufficient size to stand up to the male.
They have spawned several times so far and as tlindsey stated the male can be aggressive during the interim. Saw an interesting activity yesterday. They had spawned last week and ate the eggs again. I walked by the tank and saw they had each other by the lips and were fighting. This fighting went on for several minutes. They lunged at each other with strong impacts. They bit at fins and body parts. They locked lips a few times in what looked like a wrestling match. The female appeared to damage one of the males long trailing ventral tendrils with a deliberate bite. It is bent now anyway. The male finally did give and retreat to the other end of the tank. The female went over nd gave him a final nip.
This was the first and only time I have seen such a fight with angel fish. They usually stop whatever they are doing and look for food when I am near the tank, but not this time. I considered removing the male again but do not have a tank ready. At any rate they are now getting along fine again. Apparently the female understands she does not have to run and hide anymore. It is an interesting hobby and even after 50+ years I get to see stuff new to my experience.
I agree with the suggestion to separate them and bulk up the female. It may take a few months.