They have some nice, easy to take high chair styles out there too - some clip to the table, others attach to the chair. that may be the easiest, use the same thing at home so she knows it is "dinner" time in that seat - and now that she is starting to sit easier she may like to be able to look around.
The other thing I have done is take the LO out of the seat while we order and wait for the food and save that "20 minutes" of quiet for when the food gets there and is hot - we can usually get most of the dinner eaten quick! That way he is in my arms and bouncing around when I am not trying to eat
Also, as she get a little older, you can try some finger foods to help extend her happy time - cheerios, a sippy cup, teether biscuits - check with your dr before you give solids, but she is getting close I would think!
Hope that helps!