I have some funny friends, one teasing the other by using German to talk to her, even though it is knowledge that the 2nd gal knows Japanese as 2nd language.

So, friend 2 is asking for translation to respond and my German isn't quite up to it... maybe someone can help?

This is the desired message:
"Dear mama bear. Thank you for letting me stay with you at the hotel. I will miss your cheerful greetings in the morning and your humour. Thank you for taking care of me at Disneyland. I love you dearly, and hope to see you soon!"

Have you got an answer already?

"Dear mama bear. Thank you for letting me stay with you at the hotel. I will miss your cheerful greetings in the morning and your humour. Thank you for taking care of me at Disneyland. I love you dearly, and hope to see you soon!"

Liebe Mutti Bär! Vielen Dank, dass ich mit Dir (did you stay in her room? you could also use "bei Dir") im Hotel übernachten durfte. Ich werde Dein fröhliches "Guten Morgen" schwer vermissen, ebenso wie Deinen Humor. Danke, dass Du Dich so toll um mich in Disneyland gekümmert hast. Ich hab Dich wahnsinnig gern/lieb (do you like (gern) her or rather love (lieb) her?) und hoffe auf ein baldiges Wiedersehen.

Just adding a tiny correction:

Liebe Mama-Bärin [just an alternate suggestion]! [...] Danke, dass Du Dich so toll um mich im Disneyland gekümmert hast. Ich hab Dich wahnsinnig gern/lieb (do you like (gern) her or rather love (lieb) her?) und hoffe auf ein baldiges Wiedersehen.

"ich hab dich wahnsinnig lieb" can also be used in a "non-love" situation, just very close friendship, betwen m/f as well. For instance, you DO NOT want to hear this from a friend you've just confessed your love to, because it will probably be followed by "but I do not love you in that way".

I'm not so sure about "Mama Bärin." It's a bit strange to pair Papa Bär and Mama Bärin. I'd say Mama Bär is it.

As for "im Disneyland" -- that's all right, although "in Disneyland" is acceptable too. Besides that, I'd change the sequence: "Danke, dass Du Dich im / in Disneyland um mich gekümmert hast." Please also note that the original English text doesn't say anything about the degree of the care-taking, so actually there is no need for "so toll," although it may make sense und sure sounds nice.

right, just wanted to add a "special note" to it as from the whole text i thought to read a special thank you to a special person. from the hard facts of words CG is right.