Debbie, I don't know how ceramic or porcelain compares to Corning Ware, but years ago when my mom had quite a collection of Corning, she would use Elmer's glue when it broke. I don't know if it was from heating it or what, but it held together just like it had never been broken. Even through cooking and washing (can't remember if she put it through the dishwasher or not).
Come to think of it, I have a pair of cute little mugs I bought for my kids years ago. I dropped one and broke the handle off and remembered my mom's glue trick. I've never put these through the dishwasher, but the glue has held and you can barely see the crack.
Also, I've been using a glue from Golden, I think it's actually called a "medium" but it I haven't found anything yet it won't hold. It's awesome stuff!
Best wishes with your treasure; I know how you must feel!

You might consider adding something pretty to that chipped area... like a cute little creature that hangs over the edge. The kind you might see on a clay pot. I'll post one here... it's obviously too large for a mug but it will illustrate the idea.

Or grow a small plant in it... the foliage would cover the chipped area.

If the mug is a keepsake that won't be used for drinking... I'd use Polymer clay to repair the chip.

If the chip is small it shouldn't be too difficult to mold and smooth the clay to match the mug. You might have to mix a little tole paint into the clay in order to match the color.

Once you've done that you'd just bake it and then wet sand it with 400 grit... and then 600 grit sandpaper for a few minutes. Then buff it till it's as shiny as the original mug.

I'd mask off the original mug before sanding... wouldn't want to scratch the surface.

Let us know what you decide to do... and good luck :)

Here is a link that might be useful:

Lia... Unfortunately, I don't have the piece to glue. But, Thank you so much for your kind words!
Candy...You speak like a pro! Where would I find the supplies you mentioned? Is there anything that can be used that you would be able to drink from? The plant and little character are also great ideas. I'll post pictures when done! My husband bought me this mug right after we saw our first Grandchild...It saws "Grandma" on it! We are awaiting Grandchild #6 now...I cherish them all, but seeing the first one was a meeting I'll never forget! So...I guess I don't HAVE to drink from the mug! Funny how we get attached to little things.

Thank you both! Debbie

Candy~~~That is such a sweet offer, but you don't need to go that trouble. I'll check at our local Michael's store and they probably have what you have described. I've printed your instructions to take with me! Thank you so much...I appreciate all your help. If I get stuck, then you'll hear from me sooner than later!
Thanks again! Debbie

Why don't you take it to your local green ware dealer and have her repair and fire it for you. It would cost a little, but probably no more than $10 - 14. and it would be just like new and safe to drink out of.