To be honest, probably a bit of both – sometimes genuinely too engaged to hear you (they mostly have 'single channel attention' at this age and so their ears do more or less turn off if they're focused on something else), sometimes choosing not to do as asked.
Tips: You basically have to be prepared to constantly save them from themselves at this age. Either be in a safe space/'yes' space like a soft play or well-toddler-proofed room (or strapped in a buggy), or you need to be very alert and close enough to intervene fast! If she's fast and a bolter, you may need reins.
For stuff that is not ideal, but generally not dangerous, it helps to accept that she's going to taste-test the sand, the grass, her own sandal, etc., like many, many babies and toddlers before her. Yes, intervene, but don't beat yourself up over it.
Tantrums: At this age, very brief sympathy and acknowledgement 'Oh, you're upset you can't have X' and distract, distract, distract. Most of them are still pretty distractible at this age.
Depending on how communication is going, baby sign language or Makaton can help with frustration because they can't make themselves understood – even a handful of signs can really help, especially for things that aren't necessarily early spoken words, things like eat, drink, more (both of mine also used 'more' to mean 'want'), all done, tired. If she's already using gestures quite a bit and saying a few words, signs might not be worth it at this point, though.