So are you trying to raise the seat height because your daughter is growing? Those bike are designed for up to 55-60 pounds and even if you could easily "lift" it, the rider weight would be too much. Not saying it can't be modified but you are talking a lot of work and engineering to get it right.
PW50s are entry level bikes to get kids hooked on riding. Once they outgrow them it's time to look for a bigger bike. If you let us know her skill level , weight , height, can she use a clutch?, etc, we can point you in a good direction for a replacement bike.