I think my girlfriend is jealous of my relationship with my father

I (22F) am in a very healthy and loving relationship with my girlfriend M (23F) for over a year now. We always discuss all of the problems we might encounter and we solve everything together in a healthy and mature way. But I still feel like there’s one problem we avoid at all costs.
I’ve always been very close with my family, even the most distant relatives. My mom and I spend at least half an hour talking on the phone with eachother daily since we live in different countries. I have never been that close with my dad, though, but it’s all changed recently, when the war came to my home country. My father, being a proactive person, joined the military on the very first day. I was worried sick about him, but still supported his decision. And I’m very proud of him for doing that. We became much closer after that, even started saying “love you” to each other regularly (we never did that before). He can’t call me or text me often since there can be no service where he is at the moment, but we still keep in touch.
When it comes to M and her family — it’s quite the opposite to my situation. She was never really close with her parents and siblings, left home as soon as she could and rarely talks to them now. Her father was very abusive of them and it took M a while to open up to me about that issue. Her father passed away a few years back though, so her family found their peace at last.
Today my dad called me for the first time in a few months and I was very happy to hear his voice. We talked for an hour, probably, before he had to go. When we were finishing the call, M came home from work. She silently laid her head down on my lap and listened for a while. I said “love you, bye” to my dad and he hung up. I smiled, but then noticed that M was crying. I asked her multiple times why she was upset, but she refused to tell me. After a few hours I asked her honestly if it was because of my conversation with dad and she said “I don’t know”. I feel like M is a little jealous, but not it a bad way. It just upsets her that her family is not like that, probably.
How can I make things easier for her?