S.B.
You don't say how old your granddaughter is.
I used to cry every single time I had to leave my grandparents. I would say I didn't want to go home. It's not at all that I didn't love my parents or love being with them, I just really, REALLY adored my time with my grandparents. I would have been perfectly happy if we could have all lived in one big house.
I'm a grown woman with a grandkid of my own on the way and I still hate good-byes. I am very sentimental. My sister moved away and I got to see her a few weeks ago for the first time in over a year. You guessed it...I cried and told her I didn't want her to go.
I'm not sure about the entire situation since you don't give many details, but I think it might help for you to say to your granddaughter, "I know you don't want to go, and that's okay. But, you know the time always comes. We had a great time and we'll have fun next time too. I'll miss you. Now, give a kiss and let me see a smile on your pretty face before you go. I love you!"
In the absence of anything bad going on at home, you shouldn't assume that she loves you more. You wouldn't want her parents jumping to that conclusion and feeling bad either.
Sometimes little kids just have a really hard time going from one situation to the next. I don't think seeing her less would help.
It's kind of like when moms have to drop their kids off at daycare even if they cry. You just have to give a kiss and hug, say you'll be back and keep the good-bye short and sweet.
Hopefully, it will get easier over time. She may always have a tough time saying good-bye though. I never completely grew out of it.
Best wishes.