What a lovely start. I don't think you need an accent chair, but it wouldn't hurt. If you are happy then, don't let your Mom push you to get something you don't want. I will say that it does make sense when thinking of a conversation. Another idea would be to move the corner piece of the section to the opposite corner to use as a chair. My Mom did this when I was a little girl with her sectional that was very similar to yours. I loved sitting on it. She had square table that went in the corner that was the depth of the sofa.

I'd be inclined to add some kind of low divider--bookshelf, cubbies, buffet-type console with a solid back--to create more of a sense of entry. THEN if that corner by the window still felt nekkid, I'd add a chair. I dislike front doors that just dump you into the living room, though. :)

I like the bookcase suggestion and maybe a nice plant. You have plenty of seating and don't need anymore. The configuration you have has some tv watching, some quiet sitting and is coversational all by itself. I don't think it needs it, but you could balance out that other corner