I am 95% sure that Wanda could find a way to give that order, despite all the rules regarding Loyalty, etc. Wanda is obviously conducting some serious moral juggling with her actions; she can pull it off.
Wanda wasn't in the MK. She was captured by Stanley, just like Jack.
She absolutely needs to have another side to flee to before she can do anything crazy. If Stanley dies and she isn't in a city, then she auto-disbands (assuming no plot/pliers armour). Even if she is in a city, the city would freeze and then be overwhelmed by enemy forces.
Wand is "of the lost Croatan tribe," so like Vurp she might be the chief of her tribe by default. That's not as good as being a royal like Jillian, but would still give Wanda a "side" at any time she choose to break. Just thinking out loud here, but I think it's one possible direction the plot might take at some point.
I am not so certain and I think Wanda isn't either. I don't think it was for love that she didn't want Ansom seeing her crook his dad and lover, she sees evidence of weakening loyalty.
She got burned in book 1 with Jillian loyalty spell breaking, partially because of love.
IMO she has something stronger than a suggestion spell on Ansom, but it is finite/breakable over time.
There are probably good reasons why Wanda's order for Ansom to stay back is not a bad order. He is wounded after all, a bit emotional, so if you are gonna bring emotional leaders along it's best to bring just one, the fully healed one. Also, Wanda's probably hedging her bets and ordering Ansom to strengthen the rear of the army.
So maybe Ansom thought that this order was bad for him, rather than the side.
There's also another possible take. I think Jack could inform Stanley if Wanda's order was detrimental to GK (see linked post and a couple above). So let's see what Jack has to say about it too.
Best possible plan given a *specific* question. They have initiative, time to plan and act till they end turn.
There are more ways to win a war than direct attack, eg diplomacy to split up the coalition.
Given complete control of GK, without Stanley to screw things up, it may be tempting to make deal with Hagar to let them take over Jetstone, focus on any enemies that are determined to wipe you out, and try to seem non threatening to the rest.