I'm not a veteran myself but two useful tips I could suggest are.
A combo, grab, down throw, jump, up air, double jump and up air again, after that when your opponent's falling you should be able to land some more hits.
Try and keep to the air, it's why that combo is good imo. Her side B pushes enemies back so if you feel cornered use that, if you see the opportunity to stun with her gun use it, you can lead into that combo I said earlier, get pot shot damage with an A combo or forward smash.
Hope this was helpful to you!
Said combo also works with Fair, although it works best on heavyweights.
We have 3 actual kill moves: UpB, Fsmash and DownB's kick. From the middleweights onward, Down throw - jump - UpB usually kills at 100/120 (EDIT: I just tried it against a Pikachu at 60% and it kills from the sides of the stage! Now I killed a Bowser with 85% before the throw from the middle of FD! I think I was being way too conservative with this combo) depending on the opponent. But be careful, after racking up too much damage the opponent goes way too high in the air after the throw to hit UpB reliably, although it could also be vectoring.
Apart from these, we have DownB, which is a more flashy and ineffective move. If you land it on a grounded opponent you'll bury him (which I usually follow with an Up Smash or a tilt), but if you manage to hit your opponent in the air he will usually fall to his death at rather low percentages (under 100!). This is VERY hard to land on most people. I used to abuse it at first and got rekt every time, it's when you keep it as a surprise that it works best.
DownB is a great tool, but I had to work on Training mode before I could reliably direct it (I'm on a 2DS, though).
Also, I believe Up tilt is a hidden gem. F tilt is no worse.
Since I use Fsmash early to rack up damage, I found the Neutral B - A - A - A combo really useful to refresh it.
When short hopping I mostly use forward A, but that's just me.
If you have any more questions, just ask! I'm by no means a pro (I'd say I'm actually way below what seems to be the average level here) but I'd gladly contribute!