Make sure to check your surroundings on your way to the crypt and you will find Vantage point #33 - Telescope.
There are linked stores opposite the entrance to the cemetery. Locate a safe inside one of these stores and use three lockpicks to open it, receiving several hundred silver eagles in return.
Once you've searched the stores enter the Memorial Gardens (point number 2 on the map). Explore the cemetery thoroughly and familiarize yourself with the locations of nearby tears, because they will be very helpful in the upcoming battle. Enter a terrace from which you can see the flames. There's a locksmith's set next to a burning carriage. It's also a good idea to collect a Volley Gun right now by opening a tear located near the wreckage.
Approach Lady Comstock's crypt and find a smaller unnamed tomb to the right. Use the Devil's Kiss vigor to light the torches located on both sides of this crypt, unlocking the entrance. Enter the tomb and pick up Gear #31.
You may finally go to Lady Comstock's crypt. Open a mini-tear that appeared in the lock. Ask Elizabeth to break the lock and head inside. Listen to the conversation with Elizabeth and open the padlock of her mother's coffin.