Erin Blakewood seems to be very intelligent. She brings in a poster of The Periodic Table of Elements when she moves into the Anubis House, which also supports the prediction that she's very into science. She was only one out of the new members to quickly realize that Sibuna is Anubis backwards, something that Mara did not notice. This is because Mara was more focused on solving the mystery then picking out the smallest details like what Erin did because they weren't in a more dangerous situation like when Mara joined. She seems to be the friendly and innocent one, who just wants to make friends and always the one who wants a plan. She makes sure none of her friends are causing trouble with anyone else. For example, she made sure Cassie kept under control after her attempt to flirt with Alfie to cause fights between him and Willow.
They were at the same middle school before moving onto high school. When moving into the Anubis House in The Touchstone of Ra, it seems that they're sharing a room. In The Touchstone of Ra, it shows Cassie and Erin hiding in the cellar, under a table together. It's possible that Cassie and Erin are very different, as in it's possible that Erin's strives to be intelligent as you can see in The Touchstone of Ra she's hanging up a poster of The Periodic Table of Elements, and that Cassie is very fashionable as you can see in The Touchstone of Ra, as she brings a lot of clothes with her to the house. (See Cerin)
In The Touchstone of Ra, on the trip to the museum, Cassie asked Erin who does she have a crush on, and Erin admits that she might have a big crush on Dexter. During the graduation party, Dexter comes up to Erin (and Cassie) and tells them, "I'm all your's ladies!" (See:Derin)
Erin said that she might have a crush on Dexter.
Erin's only similarity with one of the original Sibuna members is that her and Mara share the same intelligence.