Mary's opportunities did not narrow to nothing when she had children, nor are we speaking of post-natal depression when her sons are walking and talking four- and two-year-olds.

If Charles Musgrove suddenly had the sense and ability to want to support Mary as an individual, taking her on a vacation would be much less useful than having her learn some skill to which she would have to apply herself to master, or giving her some responsibilities that would be useful, and make her feel needed. Unless by recreational opportunities you mean like Anne has made for herself in her music, I still do not agree.

No one expects Mary to soldier on without any stimulation; they expect that an adult woman can find sufficient stimulation in a situation that includes society, opportunity, and security, if she would only seek it out for herself.

The text, by the way, says [Charles and Mary] might pass for a happy couple (ch. 6), so I am at a loss as to why you think Mary's marriage unhappy (without her making it so herself). All the couples, including the senior Musgroves, are described as less happy than the Crofts, if that is your source, so I do not see that as a very persuasive argument that hers is a notably unhappy match.