Gwen Stefani was at the Wimbledon, is she interested in Nadal since he won his first Wimbledon title?

No, Gavin Rossdale is a recreational tennis player and maintains friendly links with Roger Federer, Gwen Stefani being married to Gavin accompanied her husband to support Roger Federer in clinching his sixth Wimbledon, hence she was in his player's box. Probably unless the 2008 Wimbledon men's singles trophy is made out of solik pink argyle diamonds [which it isn't], sorry but I highly doubt Gwen would divorce Gavin and go for Rafael.