My 3-year-old started to stutter and it's getting worse. When do I worry?

My 3-year-old started to stutter and it's getting worse. When do I worry? Neither my husband and I stutter, but our 3-year-old daughter just began doing so a couple of weeks ago. Daycare isn't concerned, pediatrician isn't concerned (said it's only a problem if she's approaching 5 years old), but our daughter gets noticeably upset and more frustrated as each day passes. She gets stuck mostly on prepositions (I, me, the, but...) as she's thinking about the next word, trying the word 12+ times before getting it out. She starts increasing the volume of her voice to the point of yelling as she tries to work it out. Eventually, she'll get it, but there have already been a handful of times where she is defeated and gives up, looking very upset. Here's an example, how she will say "Why are you wearing a dress?" "Why-why-why-why.-why-why-why-why-why-why-why are you wearing a-a-a-a-a-a-a-a a dress?" We already know not to finish her sentences for her, and if she gives up to calmly get her to try again... but I feel like it's getting worse every day. Should I reach out directly to a SLP myself regardless of what our pediatrician told us? Or is it really not a big deal yet?