I´m worried

Just got home from work, walked the dogs, starting checking YT and then I notice Nena acting weird.
When I turned around and saw her, she was pulling something..
I stopped her and she stood up, when she stood up I saw hair from her tail missing

I always leave the hair on her tail on the same length and you can clearly see that it's not at the same length..
I'm afraid she was pulling her tail hair

And I'm scared it might be the advantix! But I can't know for sure because she was in heat the last couple of weeks and most of the times when she is in head she starts biting her behind legs or starts acting weird and I have to constantly keep an eye on her.