She'll ask you to kill EVERYONE in town using the knife and mask found in the dog house (which is in the garden of the abandoned house. So pick this up and go on your rampage slicing everyone up with your culinary skills. Once everyone is dead, head back to Betty to be allowed to exit the simulation and meet up with your father again.
The Waters of Life
Once you're out of the simulation, have a chat with your father and he'll tell you that he needs to head straight to Rivet City to talk to Dr Li in the science lab. Follow him out of the vault/garage and fast warp back to the city (your dad will be perfectly safe when you do this). Now head to the Scientist's room in Rivet city and your father will have a chat with Dr Li. He'll ask you to join him, so make your way (via fast travel) back to the Jefferson Memorial where you need to reach the Rotunda room again and meet your father there.
Now, before you enter the memorial, you'll have to re-equip your guns again (as they've been removed from the D-Pad by the game for some reason). Now head to the Rotunda and equip a good weapon as a Super Mutant Brute will be waiting for you down here. Once it (and every enemy nearby) is taken out, head back outside and tell your dad that it's safe to enter. Now head back to the Rotunda and ask your Dad what you now need to do. He'll tell you to head to turn on the Flood Control Pump Power.
Now you should head to the sub-basement of the memorial and make your way to the room with the solid marker in it, with the activation switch sitting in the corner. Hit it and then head back to your Dad so he can give you the fuses, where you'll need to make another trip back down into the basement. Again, head for the marker on the local map, place the fuses in their slot and head back up a level and you'll find the large mainframe door near the caged-off area.
Boot up the mainframe computer inside here and head back out to the intercom on the wall near the steps leading down a level. Your Dad will then tell you that you need to clear a blockage in one of the pipes, which is located right opposite the entrance door to the Jefferson Memorial. Head inside and make your way to the end where you can activate the pump control. Get some weapons ready as you'll now have to fight your way back IN to the control room where your Dad is, against a bunch of heavily armed Enclave soldiers.
Head through the now unlocked grating ahead and back into the sub-basement of the memorial building and sneak out of the tunnel and into the room below. The best way to take out the laser gun-wielding Enclave soldiers is to blast them in the noggin' in VATS with your better weapons. Head back to the Rotunda and once the next scene is over with you need to lead the scientists back to the secret tunnel. Make sure you have enough health and/or drugs to take out the army of soldiers and Feral Ghouls that will hinder your progress.
Follow Dr Li through the Taft Tunnel (via the manhole) and lead the way down the tunnel (take the right hand path) down to the terminal which Dr Li needs to unlock. In the adjoining room area couple of Enclave soldiers up above, but if you stay out of their line of sight beside the terminal, you should be fine.