If your current agent is the one who showed you the builder's displays first, then she might be due the commision or at least a partial commission as the procurring cause, so you need to make sure that if you use a second agent they know the first agent was involved, so the first agent doesn't sue the second agent. I would talk to her first, and just let her know that you aren't sure that you are comfortable having her represent both sides and are considering using a different agent and how would she handle it.
Carefully. In most cases your agent already knows enough information about you to use it against you, but she is also contractually obligated to look out for your interests on your sale.
I don't know the policies or procedures for MO, but this could be a dual agency scenario or she could represent you on the sale and the builder/husband on the purchase or she could refer you to another agent.
She would have a lot on the line to make sure she does everything properly, the risks are high, but it could be done. Tell her what you are contemplating and ask her how she would suggest you proceed.