Okay, after losing a couple of times I decided to give every member of my team a magical seed, to even the playing field. This made all the difference, this is how it went.
She started with her alola Sandshrew and I started with my Metagross. It would take just over two hits with meteor mash to get it down, but I knew she would use a super potion after the first hit, so at the same time I used a full restore and did it again. I got sandshrew down pretty easily this way, although my Metagross had a lot of damage because of her eathquake.
She put in her Excadrill and I put in my Rotom. We both had magical seed, so our first turn would be pointless. For this reason I used this first turn to us another full restore on my Metagross so my team would be full health again. The next turn I destroyes Excadrill with hydro pump (not to much damage).
Then she put in Mega-Scizor, a strong pokemon of hers. I forgot what was strong against it, so I put in Gyarados, who got owned in one hit... Then I put in Porygon-Z who did a lot of damage with zap-cannon. Porygon-Z won.
Klefki was the 4th opponent, and a killer one with her OP draining kiss... I put in Rotom and he only just survived a draining kiss... (I was able to restore Rotom to full health before starting). This is where I got sneaky. Rotom allways just survived a draining kiss and that was Klefki's only good move. I used full restore after her attack every time untill Klefki ran out of PP. After that I used my time to revive and heal all my damaged pokemon and then destroy Klefki as if it was nothing...
Empoleon was easy. Porygon-Z used zap-canon and it was gone
Aegislash... My nightmare... In attack mode it OHKO'd my remaining pokemon every time in my previous matches, so I knew I had to play it hard right away.... I started with Porygon-Z who got 1 hit in and a quarter of Aegislash's HP was gone, as was my P-Z... Next was Rotom who, with hydro pump, got him half way down. Metagross did nothing, dead, destroyed as a fly... Gyarados was back and got hir right away. I thought he was gone, but no! To my happy surprise he was left with 7 HP!!!!! I almost cried a little there, hydro pump got Aegislash and he was left with only a quarter of its HP! I only had 2 pokemon left: Crobat (flying and a little useless) and Garchomp (my planned ending pokemon). They both still had their magical seed, so I thought I had a good chance.
First I put in Crobat, a little bit of small damage, even if it was just 10 HP, every little bit helpt. Acrobatics, nice, quick, but I got a surprise here... It did more damage then expected! The Garchomp I saved for last WITH a magical seed stayed useless on the bench! The Garchomp I grinded with against the TMNS trainer in grand hall to get him to a decent level and battle ready wasn't even used!!!
Finally I was done and satisfied and who knows, maybe I need my Garchomp in my next gymbattle