My cats mouth is red/swollen?

Hi everyone!

My cat Maisie is red and swollen on one side of her lip and it looks irritated(not open).
She had this one time before, about 4 months ago but it never was swollen like this and went away after two days.

Hope someone know what is causing this and what to do?

Allergies, insect sting? It's too vague to diagnose. She should be seen by a vet to assess the cause, especially since it's happened before.  Hope she isn't in any discomfort because of it.

Yes i was thinking allergies to or maybe a sort of virus idk but when I took a closer look and she dont seem to bother and is eating and playing as normal but its still swollen and have been all day [emoji]128532[/emoji]