What type of Mule is she? Ie., what breed was her mother? If Swaledale, she should be fairly biddable / laid back, if Blackie then yes, can be a lot more bolshy.
As a generality, Mules are outstanding mothers, and rarely give issues mothering up (although an inexperienced ewe may steal others' newborn lambs when she's hormonal, if your system keeps them close to each other and doesn't pen them as soon they lamb) but yes, that strong mothering instinct can make them bolshy with other sheep - and lambs - as they get close to their own time.
As long as you don't make her think you are a danger to her lamb, she shouldn't get bolshy with you. (So never lift the lamb(s) above her eye level, always keep the lamb(s) between you and her, that sort of thing.)
(I had ten years farming NC Mules - both Swaleys and Blackies, predominantly to Texel/Beltex type tups, lambing indoors and out - amongst other types on the uplands of Cumbria and moorlands of Northumberland. 30-ish and 80-ish respectively. So, a fair bit of exeperience!)
What breed of tup did you use? And have you had her scanned?
Mules rarely have singles, but if they do you may need to be ultra-cautious about feed, as singles can become too large to birth easily if the ewe is fed. (She will still need sugar though, so a molassed lick will be needed whatever she's carrying.) Conversely, Mules can be very prone to triplets, and with triplets, or twins to a chunky breed of tup, she will really need cake in the final 6-8 weeks as she simply won't have the room for the amount of forage she'd need for the lambs, milk, and maintaining her own condition.
Severe risk of twin lamb disease if you don't get the feeding right; her behaviour at the hay rack may indicate she is struggling...
(But they are greedy sheep, as they need to be, so it could just be that. My very experienced collie would plough me a course through 400-head of in-lamb Swales so I could follow with the feed snacker. When we went to the 80 Mules, he'd stare dolefully at me from the back of the quad - no way he was gonna be on the ground between 80 pregnant Mules and their cake... 😂)