Back to the topic 🙂.
As I remember in the Book, where Luke first meets Mara at some point he notices how she often uses piercing strikes apart from regular slashes. While Luke couldn't guess where it is coming from, author's implication was that her style is similar to Palpatine.
While Palpatine is uber skilled with lightsaber, I didn't see any evidence of him utilizing kicks and unarmed combat. He seems to be pure fencer.
But Mara on top of lightsaber combat was trained as Assassin and as result was very versatile and excelled at survival during fight. Roughly I would say her fighting skill was something similar to Maul.
She got Apprenticed by Kyle Katarn. And it didn't take long for her to surpass him. He fell to darkside at Dromund Kaas. She came to rescue and not only resisted corruption herself but fought him and successfully fended off all his attacks, he kept retreating from her.
Her speed feats are easy to evaluate. She was fast enough to fight Caedus, who in turn was fast enough to fight all-out Luke, who was fast enough to defeat Sidious. So she is fast enough for Sidious.
As Zampano gave nice recap of her fight with Caedus, it is clear that he is much more powerful, than her, yet, she showed incredible Force defenses, she resisted and mitigated his attacks as much as possible.
Caedus is not the only example of her encountering more powerful foe, than her. Together with Luke she fought Joorus C'baot. His madness gave him enormous power. He could give wide Force lightning that Luke only partially was able to block with lightsaber, the rest was stinging his legs. C'baot channeled powerful vortex of stone rubble. He, also, excelled in mind domination and made a puppet out of Luke's clone. Moreover, Luke was heavily distracted by mental noise caused by his clone's presence, so a lot depended on Mara. Also, she was nowhere near her full potential as she didn't use Force after Emperor death for years and started regaining her connection only recently. Still, she showed herself well in the fight and was the one who slaughtered both Luuke and C'baot.
The biggest "IF" is whether she will be able to defend against Sidious' Force attacks. She barely defended against Jacen. And Sidious is even more powerful. Weaker Force users can put adequate defense against stronger ones but, if power difference is too big, then there is simply no chance. We can only guess how much more powerful Sidious' instant TK attacks are, Mara would have very hard time blocking them. Even, if she can overcome them, there is, also, Force lightning of enormous strength. She can block lightning but his one might be too strong. Even Luke didn't display blocking his lightning and instead tanked it like a Boss but Mara couldn't afford to tank it. 😄
The only his power I don't worry about is mind domination. Considering her Force bond with Luke and Ben, she's got MAD MOTHER IMMUNITY.
My conclusion is that Mara has fairly good chance against him, if she manage to reach him and engage in lightsaber combat. But, if he utilizes his offensive Force attacks as frequently as Jacen, then her chances are very small.