Need help with plane carry on ?!?

My mom wanted to buy a big tote bag so she can fit her blood pressure machine and other stuff that we might need because we are waiting 7hrs in panama untill the plane is ready i guess.. will they like say something about her abnormally huge bag? its no monster size but its like one you can bring to the beach or something soo will they like say not to bring it on the plane or should we get a smaller one? lol here is the exact size of it.. a href="http://image.rakuten.co.jp/bigapple/cabinet/kitson/kitson01.jpg" rel="nofollow"http://image.rakuten.co.jp/bigapple/cabi…/a