While every pastor's wife is different, so are the seasons they are walking in. And with that comes different needs. So as far as what you can do to better serve them, I would pray about it, and figure out the seasons they are in.
For instance, one may have small children and may not have had a date in a while. She could probably use a babysitting offer. Or she could use some help on Sunday mornings, because often times us pastors' wives are single moms on Sundays.
One Pastor's wife may carry a lot of responsibility serving on a Sunday morning and misses sitting and enjoying listening to her husband preach. She may could use the Sunday off, and have you replace her so she can relax and get back in the sanctuary with her husband.
Another may just need a gift card to go treat herself. Pastors' wives often give all of their time and energy to their kids, husband and full time ministry and forget to treat themselves on occasion. This would bless her tremendously.
Last, encourage her!! She needs to hear she is doing great. She needs to know someone is "for her" and cares to help in anyway you can. Let her know you are willing to help in anyway.
xo a girl who sleeps with the pastor