Well, for 2.5 years, I did home daycare for kids before I had my 2nd child.... and before my eldest went to Preschool.
1) your "home" is also your daughter's home. And her personality is like my Daughter's.. at that age. Normal. Its fine. Don't try and scold for it or change her. Not saying you are... just an aside.
2) It is 'her' home TOO... so, yes, young Toddlers can or may have issues about other kids being in 'her' home too.... because then 'her' things/toys are up for grabs, her routine is different, her Mommy is not 'hers' only... etc. And at this age, and you being pregnant... a young Toddler needs their Mom in different ways and they get anxiety/stress and even separation-anxiety... even if you are there. They have to "share" their Mommy with others.... and they may be side-lined. Thus... they act-out. They act-out... Because: (a) their emotions at this age is NOT even fully-developed yet, (b) they do not have automatic coping-skills to deal with their emotions (c) They don't yet know how to succinctly communicate or express themselves (d) they do not yet have full impulse-control (e) they don't know how to deal with frustration or sadness or anger... yet in a perfect way (f) they don't, when needing attention, know how to get it.... in a way that is appropriate.... yet.
3) ALSO... with the other kids around... SHE may get: (a) over-stimulated (b) tired (c) just wanting time to HERSELF... but with all the other kids around... she cannot do that. Hence, a young toddler gets frustrated and tweaked, too. Her time.. is not her time... it depends on all the others and their needs.... with Mommy and the environment....
4) If the other kids are bold/in your face/extroverted/more aggressive than she is... then sure.... .like an adult... being around that kind of kids can simply be... irritating.... hence she may act-out.
5) Your daughter... is being her age.
She is trying... to deal with everything.
She is young..... so she is not completely in control of everything nor her own navigation of it of all the things/kids around her.
6) Sure, 'discipline' is used. To enforce rules and behavior.
BUT... unless you TEACH a child problem-solving or coping-skills or alternative ways of expressing frustration... just punishing or disciplining... will not address, the child's 'skills' in managing difficulty or frustration. Do you see?
AND you need to console her... in that it is OKAY for her to TELL you things, anything... and to express herself TO you. And it is okay... she will not just get punished for it.
(7) PLUS, you have a baby coming. THAT is something that will change her life, too. AND her Mommy.
When I was preggers with my 2nd child... I spent a TON of time on my eldest.... it was not 'my' pregnancy... but a time for my daughter... to have me and for me to explain things to her.... we took photos of her with my tummy, she talked and sang to her baby brother in my tummy, I explained what a baby does (it cries, it wakes at all hours, I will nurse him etc.), but its OKAY... because Mommy is still her Mommy and it is my job to care for baby... so she does not have to worry. I took her to all my prenatal appointments... which my Doc encouraged. He even taught her how to put the Doppler heart monitor on my tummy. She REALLY BONDED with her baby brother... while he was still in my Tummy. I spent my pregnancy... not on myself... but in "prepping" my daughter AHEAD of time.... so that she felt at ease with me/baby and all that will happen. Once her baby brother came home... it was not such a 'shock' to her then. She really adjusted well.... by then.
You do not help the eldest adjust to baby... ONLY once it comes home. You prep your eldest... NOW.... while you are pregnant.... now.
all the best,
Susan