الزميلة دي شرحت لي المشكلة، وانا فهمت منها.

In Egyptian Arabic, demonstratives like ده / دي / دول often come after the noun.

So:

• الزميلة دي = this colleague
• literally, it looks like the colleague this

This is a very common Egyptian pattern:

• البنت دي = this girl
• الولد ده = this boy
• الناس دول = these people

Also notice that the noun is usually definite, so you normally get الـ on the noun: الزميلة دي, not usually just زميلة دي.

If you put دي before the noun, it usually changes the structure and meaning, often toward something like this is the colleague depending on context.

Because الزميلة دي is a definite phrase: this colleague.

In Egyptian Arabic, when you say this + noun, the noun is usually marked as definite with الـ:

• الزميلة دي = this female colleague
• الكتاب ده = this book

So the pattern is often:

• ال + noun + demonstrative

That is one of the most basic noun patterns in spoken Egyptian Arabic.