I have not been in that cabin, but it's quite a long way back so might get some engine noise and vibration. Seasickness should not be a problem she is a true ocean liner not a cruise ship. I am sure you will have a great time on the most famous ship ever.
Sorry dont know that cabin either, we have always been on 1 deck but as far as seasickness goes I agree with Crooks; you are most unlikely to suffer it on QE2. I have balance problems following an illness a few years ago and have needed a phenergan injection from the ships medic( which I fully recomend if you should feel unwell) but have never had any problem on QE2 or QM2 and we have been in some pretty bad weather on both. Have a great time.
I couldn't find cabin 2153 and I looked at 2007 brochure. Am I mistaken? But you should certainly enjoy the Princess Grill and if you are lucky enough to get bumped up into Queen's Grill, which happens occasionally, you'll enjoy it even more. The rest has been said by Cynthia and the Crooks. Neil.