Hey Momma,
I think its just her age but you never know.
luckily you know about his family ahead of time.
I suggest try to introduce her to and expose her to various ways she might feel clausterphobic,
LIKE try covering her head with a blanket. both of you get under and make the experience fun for her. use a flash light.
Then graduate to building a fun fort out of the sofa cushions, and cover her it with blankets.
GO inside and make it fun for her.
putting her doll house inside it and make like a mini home.
then have and indoor CAMP OUT. during the day, and then again at night. OUTSIDE.
and make it fun.
Afterwards try adn find a BIG BOX
( like a refridgerator box)
Cut FLAPS not holes. For her to peek out of, and make it fun for her.
And last is playing hide and seek in the closet.
this works best with an older sibling or cousin, or friend.
( such as a 9 year old neighbor)
Start with cleaning out the bottom of the closet so she can easily fit with room. and tehn laugh when you find her.
Do it daily and she will enjoy it.
and you can SLOWLY fill it back up with things, making it smaller. but slwoly so she gets used to the smaller space gradually. and doesn't realize.
Closet then try it with a diffrent closet.
that is only halfway empty.
And then try riding an elevator with music.
and NO PEOPLE>
pretend your going for a ride,
and LIFT her up in your arms before she asks you to.
and just walk in there real calmly, and only go up one floor. and get off real quick. and continue to hold her in your arms till you round the corner and the elevator is no longer in sight.
do this everyday for a week till she gets used to it.
then the following week try walking onto the elevator without lifting her. and see what happens.
IF she is fine then you know she is Fine.
If not then keep bringing her onto the elevator everyday till she is fine.
Good luck
M