She does this because it is working for her. It is a form of control.
She tells you to say you love her. You do it. She feels better. Why would she stop this behavior?
Let's look at the problem briefly. What is the meaning of "love" for you?
Is it conditional?
Is it delivered on order? Like a pizza?
Or is it something else? What is it? Write down all the points you can think of that help you to describe love...
Is love freely given? Without condition?
She has trained you from childhood. But now, it is hard to untrain oneself as an adult. If she tells you to jump, you jump. It feels wrong to go against what our parents have taught us. But your mom telling you to say that, was just wrong. It also felt wrong for you to say it when you didn't feel it. It wasn't authentic or freely given.
In that moment when she is challenging you, and using this control technique to get you to say what she wants to hear, one way to respond is with humour.
"Hey mom, I'm having a bad day today and can't tell anyone I love them. Gotta go! See ya later alligator!"
Hey mom, this love bird's not feeling the love today. Gotta fly!"
"Love isn't a pizza delivery service mom. I gotta go - see ya later!"
Then get out of there before she has a chance to get her engines revved up to nuclear. You'll only have a few seconds while she is in shock from your reply.
Then practice distress tolerance, and LET HER have as much time as she needs to self-soothe. Don't communicate with her until you have reason to believe she is feeling better.
Another way would be to respond rationally, and point out that love has to be given freely, and isn't really love if those words are spoken because of a command.
But that would probably escalate it into a big argument. In my experience,
rational responses that JADE in any way escalate. The outcome would likely be an all-out blow-out.
I would stick with humour. The effect of surprise (she won't be expecting it) is powerful, and the humour generally has a de-escalating effect as long as it's not insulting or condescending, so it's important to keep it just silly and fun.
What is this behavior? Please help me understand.
This behavior is the child in her. She "grew up" physically to be an adult. She probably "grew up" intellectually. But her emotional development got stuck in childhood (proabably from some trauma). It becomes problematic when a child grows up, take on adult jobs and responsibilities and relationships and daily decisions, but their emotional development is still stuck back at the age of a 9 year old or a 14 year old.
Something made your mom feel bad. It could have had nothing to do with you. It could have been a look or a smell or something the cashier at the grocery store said. Or maybe there was some relationship struggle between the two of you. Regardless, there was a trigger. Then she comes to you to make her feel better by demanding you tell her you love her. It was utterly childish behavior.
Instead, give her time to sort her own emotions. She is an adult. She needs to be granted the opportunity to solve her own problems. It is
not your job to parent her every time she feels bad. Let her self-soothe. It's the best thing you can do for her. Besides, it sounds like she could use more practice soothing herself.
My mother once put on her 6 year old child voice in full "waif" mode and said to me "will you be my mommy"? She was about 84. No way I was taking that bait. I responded with humour, and that was that.