It’s my opinion, that BLACK WIDOW was planned to be Spencer’s twin, Alex Drake. Let’s look at the facts about this-
1. MK said she knew who the final A would be when PLL first started. It’s possible that MK just didn’t tell anyone her idea until later, in case it changed.
2. If you look at the opening of PLL you’ll see that Spencer’s original dress matches the one in the coffin.
3. One of the twins from Alison’s story in the first secret, had birthmarks just like Spencer does.
4. MK tweeted that the lady in black was PLL endgame. The stand in/double for this character matched Spencer’s physique perfectly. There is no way Sara Harvey was PLL endgame. She’s literally the most unimportant character on PLL and she’s DEAD.
5. Veronica once mentioned “SPENCER’S EVIL TWIN when talking to Spencer about her drug use.
I think when the show aired the episode with Wilden’s funeral and the first appearance of BW in episode 4x01, that this was definitely supposed to be Alex getting into the limo with Charlotte. This would have FIT THE STORY PERFECTLY. When Charlotte found out about Mary, she also found out about Spencer and Alex. I think in this case, both Charlotte’s and Alex’s motives could have been almost the same. Both of them had missed out on having a family like Alison and Spencer. Alex would have been who helped her in the dollhouse, NOT SARA HARVEY. When Charlotte died, Alex wanted to find her sister’s killer and after she found out she did leave but eventually became so obsessed with Spencer’s life and with Toby that she came back to try to replace Spencer permanently.
We have to remember that PLL was originally conceived as a 5 season show so showing BW at this point would have made perfect sense. I think MK’s original plan was to reveal Charlotte AND Spencer’s twin for the final A reveal. MK came up with the character of Cece/Charlotte at the end of season 2/start of season 3 and also started the creation of Mary Drake soon after. MK knew she wanted Spencer to have the twin, so with the creation of Charlotte, came Mary Drake’s story and also ALEX’S.
When the show got renewed during June 2013, for 2 more seasons, when season 5A was airing (and what should have been the final season) MK had to change up not only who who BW was but she had to make Charlotte and Alex’s reveals separate events, not together as planned because now they had 2 more seasons to fill. When MK tweeted that BW was PLL endgame it was on August 21, 2013. This was during season 4 and this would have perfectly set up Alex’s reveal as Uber A at the end of season 5 but instead MK had to change BW’s identity from Alex to Sara Harvey and wasted such a great character because PLL went on until season 7. I’ll never believe otherwise.