I have a question about MGS4?

May be...

In MGS1, Naomi swore revenge at Snake after what happened to Gray Fox in Zanzibar Land. Snake and Frank Jaeger (Gray Fox) battled in Zanzibar Land on a live mine field and Snake came out victorious, leaving Frank Jaeger with only one arm and leg. After the downfall of Frank Jaeger his body was recovered on-site by a clean-up crew. He was taken by FOXHOUND's chief medic at the time, Dr. Clark and became a guinea pig for Clark's gene-therapy project. In order to improve his mobility, an experimental exoskeleton was reconstructed directly onto his body, leading him to the cyborg ninja as he was. What I don’t understand is that if Naomi swore revenge at Snake, why did she team up with Liquid in MGS4, when she knew that Liquid was the one who destroyed Gray Fox for good?

That is exactly what I was wondering the other day!