It's tough to say what she is finding watery, however, it could be lack of a head or maybe the presence of too much sanitizer. Taking a shot in the dark. Even though its carbed, the lack of head or head retention often leads people to think the beer is watery even if it is carbed. The other thing could be getting some of that slippery feel from sanitizer. I know when I started brewing I was anal with keeping everything clean and there was sanitizer on everything. This gave my initial brews a slippery water feel even though they had a full body.
The only other thing I can think of is low attenuation. Get that silky mouthfeel and describing it as watery even when it's full bodied. Not sure what your wife drinks normally, but if they are used to the dry crisp lagers (bud miller coors, etc) then maybe a sweeter mouthy ale could feel watery to them. Just a thought. I wouldn't expect a porter and nut brown to be watery!